This invention relates to the field of electrical printed wiring board structure and to the manufacture of such boards.
Wide acceptance of the printed wiring board as a suitable mechanical carrier and electrical connector for electronic and small electro-mechanical components is evidenced by the use of these boards in most modern-day electronic systems, including computers, television and consumer electronics, military and industrial equipment. Although this wide utilization attests to a major degree of satisfaction with the performance of these boards in a variety of environmental conditions, certain problems occur frequently in complex multilayer printed wiring boards, particularly where these boards are subjected to extreme environmental stresses such as wide operating temperature range and wide frequency band mechanical vibration. Environments of this type are of course frequently found in military equipment such as aircraft where typically the change from tropical conditions and mechanical quiescence to sub-Arctic high-vibration conditions can occur within a few minutes.
An area of frequent concern in such high-stress environments is the printed wiring board arrangement for through-hole conductors which are used in the locations where electronic components are mounted on the printed wiring board or where conductors residing in a plurality of printed wiring board layers are electrically joined together or where edge connectors or other off-board electrical connections are made to the printed wiring board conductors. The through-hole conductor structure has been a frequent source of intermittent electrical connection, electrical heat generation, chemical corrosion activity and other failure mechanisms. Through-hole conductor problems exist to a degree requiring significant expenditure of extra fabrication, testing and maintenance effort as preventative assurance against expensive in-field equipment failures. In the earlier days of the electronic digital computer, for example, it was common manufacturing practice to hand-solder the printed wiring board areas attending a multilayer through-hole conductor, on each side of the board, following a normal dipping or wave soldering manufacturing procedure. Dipping or wave soldering was alone sufficient for other connections on a printed wiring board, but not adequate to assure reliable long life through-hole conductors. This special and elaborate manual attention to a through-hole conductor is clearly undesirable from the viewpoints of printed wiring board cost, reliability, appearance, and from the possibility of damaging other components located nearby on a crowded printed wiring board.
The prior patent art discloses inventive attention to the printed wiring board in general and includes the patent of R. F. Jack et al, U.S. Pat. No. 3,075,280, which depicts a method of interlocking between the insulating base and the metal surface of a printed wiring board. In the Jack patent, this interlocking method requires that metal particles be compressed and heated within the grooves of a forming die to fabricate the printed wiring board conductors.
The patent of K. H. Phol, U.S. Pat. No. 3,628,243, discloses a method for forming an isolated conductive path on a laminate by mechanically displacing portions of a conductor sheet to a locus within the wiring board cross section and out of possible connection with the remainder of the conductor material.
Generally, none of the prior art configurations provide a printed wiring board through-hole conductor arrangement that is satisfactory from all of the pertinent viewpoints.